Human pelvic girdles are pretty much unique within primates because we are the only ones that evolved from climbing in trees to walk upright. Ardipithecus ramidus remains are now helping us to understand how humans evolved to walking upright. Although Ar. ramidus' lower pelvis remained largely ape-like so it could still climb, their upper pelvis shows that they were capable of effective upright walking. Many pieces of anatomy from skeletons of Ar. ramidus are what helped us to come to this conclusion (the ilium, ischium, pubis, pelvic form, pelvic function, the femur, and the thorax). The studies of Ar. ramidus show that adaptations for bipedalism were well established by 4.4 Ma despite still being able to climb.
https://app.perusall.com/courses/human-evolution-3/99c_lovejoy_et_al_2009_the-pelvis-and-femur_of_a_ramidus
nice image here. Arid's pelvis does look a lot like Lucy's in this image! I recall reading an interview with someone on the Ardi team that was done before Arid publications came out and he said he thought she walked like something out of the "Star Wars Cantina.."
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